Bill, It is because your rounding rules aren't quite the same as the ones the software employs, so for example the software has 16.5 x 8.57 as 141.40, not 141.41, and corrects the rate to get your desired result of 141.41. Neither rule is right nor wrong.
The easiest fix is to not include the amount in your csv. But do include the comma, like this...
00234,WKD2,16.5,8.57,
Or put a heading on the csv file like this:
employee code, payment code, hours, rate, ignore
00234,OT2,16.5,8.57,141.41
etc